Take a thread from the fabric and burn it with a flame. Pure silk burns with the smell of burnt hair. When you burn the edge of real silk fabric, the flame is invisible and it will stop burning as soon as the flame is removed. The ash produced hence, is black, crispy and brittle. It turns to powder when twisted in fingers.With the artificial silk, it is quite the opposite. When synthetic silk is burnt, there is a flame and smell of plastic.